Inevitable consequences of ion-neutral damping of intermediate MHD waves in Sun-like stars

TL;DR

This paper investigates how ion-neutral damping of intermediate MHD waves can lead to the formation of cool and warm plasma structures in Sun-like stars, potentially explaining observed features like cool loops and contributing to coronal heating.

Contribution

It introduces a model demonstrating that ion-neutral collisions can generate cool and warm plasma structures, offering a simple mechanism relevant to stellar atmospheres and coronal heating.

Findings

Cool structures (<10^5 K) can form and last for hours due to MHD wave heating.

Warm plasma tubes (>10^4 K) can arise from the same mechanism.

Ion-neutral damping may be key to understanding stellar atmospheric features.

Abstract

In the context of the solar atmosphere, we re-examine the role of of neutral and ionized species in dissipating the ordered energy of intermediate-mode MHD waves into heat. We solve conservation equations for the hydrodynamics and for hydrogen and helium ionization stages, along closed tubes of magnetic field. First, we examine the evolution of coronal plasma under conditions where coronal heating has abruptly ceased. We find that cool ($< 10^5$K) structures are formed lasting for several hours. MHD waves of modest amplitude can heat the plasma through ion-neutral collisions with sufficient energy rates to support the plasma against gravity. Then we examine a calculation starting from a cooler atmosphere. The calculation shows that warm ($> 10^4 $) K long ($>$ several Mm) tubes of plasma arise by the same mechanism. We speculate on the relevance of these solutions to observed properties of the Sun and similar stars whose atmospheres are permeated with emerging magnetic fields and stirred by convection. Perhaps this elementary process might help explain the presence of ``cool loops'' in the solar transition region and the production of broad components of transition region lines. The production of ionized hydrogen from such a simple and perhaps inevitable mechanism may be an important step towards finding the more complex mechanisms needed to generate coronae with temperatures in excess of 10$^6$K, independent of a star's metallicity.